Our research is intended to elucidate the origins of specific folding and assembly behavior displayed by proteins. Proteins perform a vast array of functions that are essential for life, and protein activity usually depends on the adoption of higher order structure by the polypeptide chain. Therefore, understanding the factors that control folding and assembly, i.e., secondary, tertiary and often quaternary structure formation, for a given sequence of amino acid residues is a fundamental scientific goal. Our research employs standard characterization tools;in addition, we strive to create new tools that offer unique approaches to important questions. For example, we are developing a set of novel molecular units that enable thermodynamic analysis of parallel beta-sheet secondary structure, and one current goal is to use these tools to elucidate how basic parameters such as number of strands or length of strands influence parallel beta-sheet stability. Our unique tools in this case are unnatural diamine or diacid segments that link peptide segments via their C- or N-termini and promote parallel beta-sheet formation in water. Such linkers are not available in classical protein science, and this research requires a laboratory, such as ours, that has experience in both biophysical characterization and organic synthesis. Another chemical tool recently developed by our group, the "backbone thioester exchange" (BTE) method, offers a unique approach to analysis of sequence-stability correlations at secondary, tertiary and/or quaternary structure levels in small polypeptides. The proposed research includes the use of BTE to probe the factors that govern affinity and selectivity in side-by-side interactions between alpha-helical segments (e.g., coiled-coils). Helix-helix association is a prominent feature of protein tertiary and quaternary structure, and our studies will address previously unanswered questions in this area. In addition, we propose to extend BTE to the study of helix-helix interactions in lipid bilayers. Current understanding of the forces that control protein folding and association in membranes is underdeveloped relative to what is known about proteins in solution, and a major stumbling block in the membrane protein field is lack of effective methods for thermodynamic analysis of structural phenomena. BTE could represent a powerful new tool in this field. We want to extend our understanding beyond proteins to unnatural oligomers that display protein-like structures. Such efforts will broaden fundamental understanding of the ways in which networks of noncovalent interactions control the conformations and binding propensities of flexible oligomers. In addition, this component of our research is motivated by the long-term prospect that unnatural oligomers with well-understood folding rules could provide a basis for creating new kinds of biomedically useful agents. PUBLIC HEALTH RELEVANCE Proteins are the workhorse molecules of life. The functions of proteins depend critically on the structures they adopt, and a major goal of our work is to elucidate factors that govern protein structure. Unnatural molecules that display protein-like structural behavior could ultimately be engineered to display biomedically useful protein-like functions, and our goals include the discovery and characterization of new protein-mimetic systems.